1. Field of the Invention
This invention relates to a motor control system that carries out positioning control according to the position command of a pulse train and, more particularly, to a micro step control system for a stepping motor.
2. Description of the Prior Art
In a conventional stepping motor control system, up-count or down-count of a pulse train command externally applied is carried out by an up/down counter depending upon a rotational direction signal, data on an excitation signal corresponding to a calculated value of the up/down counter are stored in a ROM, the data stored in the ROM are converted into a voltage signal by a D/A converter, the voltage signal of the D/A converter is amplified by a drive amplifier, and a stepping motor is driven. In this construction, it is possible to cause the stepping motor to be smoothly rotated by converting the data in the ROM into a false sine wave and increasing the number of dividing of one period of the false sine wave.
In such a stepping motor control system, in order that the stepping motor can be smoothly rotated, it is necessary to rapidly carry out processing from the generation of the false sine wave of the ROM to the outputting of the voltage signal for driving the stepping motor, each time the pulse train command is generated. In a system that is comprised of hardware such as a logic IC, an OP amplifier or the like, it is possible to perform relatively high-speed processing. However, systems that are equipped with microcomputers or the like are increased at the present time for the purposes of realizing complex arithmetic operation and improving maintenance. In such a system equipped with a microcomputer or the like, it is necessary to speed up the processing of the microcomputer or the like in order that a predetermined arithmetic operation is performed each time the pulse train command is generated and proper voltage is outputted to the stepping motor. There is a problem that the cost of the entire system will raise. In addition, there are limitations of causing the processing by the microcomputer or the like to be carried out at the high speeds, so that there is also a problem that it is hard to carry out a precise control of the motor.
As a step to cope with the above-mentioned problems, there is employed a sampling processing in which a processing speed of the microcomputer or the like is realized at a predetermined cycle, in accordance with counting the step number of the pulse train command at the predetermined cycle according to the internal reference signal of the stepping motor (hereinafter referred to as “sampling processing”). However, in this case, irregular time difference is produced between the cycle of the sampling processing and the generating time of the pulse train command applied from the external and a change in the position command is generated during rotation, resulting in vibration of the rotation.